Prestressing effect of twisted fiber yarn in composites

By utilizing the behavior of twisted fiber yarn, prestressing composites can be made. In unloading, the matrix of the prestressing composite is applied in compression. If tensile load acts on the composite, the value of the tensile stress acting on the materials may decrease greatly. By twisted fiber yarn, therefore, the tensile strength of the composites can be improved. An analysis for extension of continuous fiber yarns is made here and residual stress after curing is taken into account. The prestressing intensity in the composite depends on the twist of fiber yarn. The photoelastic test and the analysis of electron micrograph are performed, and the theoretical method for calculating prestressing effect is presented in this paper.